Heterogeneous trimetallic phosphides with robust synergistic effect as bifunctional electrocatalysts for alkaline overall water and seawater splitting.

Designing a bifunctional electrocatalyst is crucial in sustainable energy installations. Herein, we have successfully synthesized an etched trimetallic phosphide of CoP/NiP/FeP (e-CoNiFeP) supported on nickel foam (NF) electrocatalyst. The typical topological structure provides sufficient active centers and multi-channel electron transfer pathway. Benefiting the commendable hydrophilic properties and the enhanced charge transfer, the composition-optimized e-CoNiFeP/NF-2 behaves exceptionally low overpotential of 228/294 mV at 100 mA/cm for oxygen evolution reaction (OER) and of 136/163 mV at 10 mA/cm for hydrogen evolution reaction (HER) in alkaline water/seawater, respectively. Moreover, the synergistic effect of functional NiP, FeP, and CoP promotes the strong electronic interaction and accelerates the kinetics, intrinsically improving durability over 130 h for OER and HER in alkaline water/seawater media. Density functional theory (DFT) simulations disclose the e-CoNiFeP/NF-2 exhibits enhanced density of states around the Fermi level and an optimized d-band center, thereby yielding the favorable H* adsorption energy and lowing the energy from *O to *OOH. Impressively, e-CoNiFeP/NF-2 provides an excellent current density of 10 mA/cm at 1.50/1.59 V in alkaline water/seawater, with electrocatalytic stability exceeding 200/130 h. The substantial research not only elucidates the fascinating performance enhancement mechanism by constructing robust synergistic effect between multiple components of trimetallic phosphides, but also provides an innovative approach to exploit high-efficiency materials for overall water/seawater splitting.